1200A Feeder Size
1200A Feeder Size
(OP)
Per NEC 240.4(B), a 277/480V, 800A feeder is allowed to be the industry standard of 2 sets of 3-1/2”C, (4)#500, (1)#2G even though the ampacity of the feeders are only 380A. However, it seems that I’ve seen this standard applied to 1200A and 1600A feeders as well, even though 240.4(C) requires any OC device over 800A to have conducters rated equal to or greater than the device rating.
So am I correct in assuming that the proper size for a 1200A feeder would be 4 sets of 3”C, (4)#350, (1)#3/0G? Or is there some loophole I’m not aware of that would allow three sets of #500's to be applied to this circuit as well?
So am I correct in assuming that the proper size for a 1200A feeder would be 4 sets of 3”C, (4)#350, (1)#3/0G? Or is there some loophole I’m not aware of that would allow three sets of #500's to be applied to this circuit as well?






RE: 1200A Feeder Size
RE: 1200A Feeder Size
RE: 1200A Feeder Size
RE: 1200A Feeder Size
insulated conductors.
75°C temperature rating is maximum required for landing the conductors in circuit breaker terminals.
If there are switches and fuses, 90°C conductor temperature rating may be considered, if the Utility permits.
90°C insulated conductor types are RHH, THHN, THHW, XHHW, XHHW-2, USE-2, THWN-2, etc. as they appear in NFPA 70-2002 NEC Table 310.16 on page 70-144. The allowable ampacity for 500MCM for these conductors is 430A.
RE: 1200A Feeder Size
You can take advantage of the higher temperature insulations even if your terminations don't allow, if deratings are necessary for >3 conductors in a conduit or in underground duct banks.
RE: 1200A Feeder Size
So a feeder protected by a 1200A breaker, for example, must have an ampacity of at least 1200A - 1199A is not acceptable. I'd suggest 4-350 kcmil copper per phase or 3-600 kcmil copper per phase for a 1200A feeder.
As others have mentioned, the upper limit of 500 kcmil is really an economic one. Beyond 500 kcmil, the added conductor cross-section does not provide a corresponding increase in cable ampacity, for a variety of reasons. Installation of larger copper conductors is also more difficult due to weight and stiffness of the cable.
RE: 1200A Feeder Size
RE: 1200A Feeder Size
RE: 1200A Feeder Size
RE: 1200A Feeder Size
If fuses are designed installed, why not to design and install the current limiting ones? They will reduce the short circuit level downstream within the power distribution system, which is always considered a safety measure as well as it prolongs contact life-cycles.
RE: 1200A Feeder Size
RE: 1200A Feeder Size
RE: 1200A Feeder Size
RE: 1200A Feeder Size
RE: 1200A Feeder Size
RE: 1200A Feeder Size
Visit
http://www.faa.gov/avr/afs/300/pdf/4d-ch11_14.pdf
for terminal lugs application and terminal blocks
http://www.squared.com/us/products/relays.nsf/07a0210021262d45862564b5006e4f84/d39ddf4c534c035585256984005f0ebb/$FILE/9080CT9603.pdf
for temperature ratings of terminal blocks
etc. for more info
RE: 1200A Feeder Size
RE: 1200A Feeder Size
RE: 1200A Feeder Size
RE: 1200A Feeder Size
RE: 1200A Feeder Size
jbartos,
See note below tables on page 31 here-
http://ecatalog.squared.com/techlib/displaydocument.cfm?id=3100CT9801&action=view
RE: 1200A Feeder Size
Code stranding on 500kcmil is 37 strand—where 600kcmil is 61 strand, making it a little easier terminate. [99NEC Ch9 table 5A]
RE: 1200A Feeder Size
This derating only applies to equipment rated less than 600 Volts. Bolted Pressure Contact Switches and 100% Rated Circuit Breakers can be terminated a 90 degree if so labeled. Running a conductor at 90 degree rating is incresing circuit losses and voltage drop
RE: 1200A Feeder Size
RE: 1200A Feeder Size
http://www.nmsu.edu/~tdi/pdf-resources/cc47.pdf
for related examples
RE: 1200A Feeder Size
Terminals are rated based on the mutual heating effects. If rated for 75C then the conductor terminated must be sized based on its 75C rating. This is because of the mutual effect of heat from the conductor and from the device. The concern is for effects of heat on the device, the connection itself and the insulation on the conductor. Using a compression lug vs. mechanical doesn't typically change the rating.
RE: 1200A Feeder Size
http://www.nmsu.edu/~tdi/pdf-resources/cc31.pdf
http://www.bussmann.com/library/docs/spd02/SPDSection04.pdf
for more info on the 75deg and 90deg conductor insulation rating and application.
RE: 1200A Feeder Size
jbartos,
See note below tables on page 31 here-
http://ecatalog.squared.com/techlib/displaydocument.cfm?id=3100CT9801&action=view
///Yes, these are safety switches in Section 3 Class 3110 with advertised lug temperature ratings 60°C and 75°C. However, I was referring to disconnect switches Section 7 Class 9422, in my posting on Mar 27.\\\